Change of ferrite core “AL” value with frequency?

[treez]

Hello,
On page 51 of the following (below) document concerning the ETD ferrite cores, the table in blue shows two values of the “AL” parameter. (“AL” corresponds to the ‘allowance’ of the ferrite core material).

One value appears to suggest that AL is 4000 when measured at 1KHz, and the other figure for AL is 5760, and suggets that this corresponds to 100KHz.

There is also a graph on page 51 which allows one to calculate the AL value corresponding to a particular core gap size. –however, this graph is quoted for measurement at 1KHz. –What is the point in having a graph for operation at 1KHz?……hardly anybody ever operates ferrite cores at anywhere near as low as 1KHz.

Also, does the AL value really vary that much with frequency?

E series document from TDK:
https://product.tdk.com/en/catalog/datasheets/ferrite_mz_sw_e_en.pdf

 

[FvM]

The difference is mainly not related to operating frequency, it's small signal versus large signal. You can refer to the supplementing PC47 ferrite material documentation from Epcos/TDK for details, also regarging exact frequency characteristic.

 

[juan_zo]

Hello Treez,

I think 1KHz is a low frecuency to work with ordinary ferrite cores, however, it depends on the density of the magnetic material in the core. Some cores are of Fe powder and others of magnetic materials, ceramic and Fe powder. For low frecuencies, like 1KHz, I think the best option is the second one like your choice (Mn-Zn).

The different values of AL are because the core work is beter at 100KHz than at 1KHz. The "Why" is capacity across the time to mantein the magnetism, in that case, your core has a proportion at 1KHz and another at 100KHz. Ok, I do not want to bore you, in short... For frequencies around of 1KHz, you need to use: 4000±25% and for frecuencies around of 100KHz you need to use: 5760 min. That is, Eg: if you winded 1 turn on the core, if you use it at 1KHz, you will have around of 4000nH; and around of 5760 at 100KHz.
It is not a problem, you can test its work easily!

I hope you can solve your question.

Have a nice day!
Best regards,
Juan_zo

 

[treez]

thanks but its disappointing they put the graph showing the variation of AL value with gap size in terms of 1KHz operation.

 

[juan_zo]

Hello Treez,

I am sorry for my last repply, I did not understand it. The graphip is all at 1KHz, I mark it at 0,1mm - 1mm - 2mm.



Check it please.

I hope you can solve your question.

Have a nice day!
Best regards,
Juan_zo

 

[FvM]

It's not surprising that most measurements are made with a LCR meter, which is the easiest way to do it. They are always small signal, changing the frequency to 10 kHz won't change much.

But it's no problem to estimate the effective µr/large signal values from these data, or calculate it accurately using respectively magnetic circuit formulas. For standard purposes estimating a linear factor should be sufficient.

- - - Updated - - -

I just remembered that we already discussed the air-gap and AL stuff two years ago https://www.edaboard.com/threads/266432/

 

[juan_zo]

Hello Treez,

I am sorry again for my last answer, I was in a hurry typing in the work laptop and going home, you know...

Well I tried to say:

"In the picture appears some values, I marked three values for 1KHz, I marked the different air gap lengths at 0,1mm - 1mm - 2mm.



Check it please.

I hope you can solve your question.

Have a nice day!
Best regards,
Juan_zo